DBMS software is designed for the storage of facts about the real world, future modifications and the searching/sorting of data. Describing the real world in an organized way is an extremely complex task, so it needs some formalization. This formalization is referred to as a Data Model.

A data model is a set of tools of a given DBMS. The data model is defined by three terms:

Data models are generally described in the following data organization categories:

hierarchical

network

relational

object-relational

object-oriented

Since every DBMS supports some original features, you could say every DBMS has their own original data model. Many DBMS have features that exist in one or more data organization categories since trends in data management have rapidly evolved from the 1950's.

Before we start having a closer look at database models let's note that data can be of two types:

Useful data (primary data). We create a database with intent to keep this data.

Internal data, e.g. required to establish links between records.

Lets have a look at each way to organize data, analyze how internal data is expressed and how it works with primary data.